Nucleic acid transfection is one of the most important tools in modern biology, and an emerging tool for biomedical applications. In our proposed research, we will use gold nanoparticles as transfection vectors. Gold nanoparticles possess three attributes that make them highly promising vectors: 1) Tunable size commensurate with biomolecular scales (4-10 nm); 2) Low inherent toxicity; 3) Stable and easily decorated monolayer surface, allowing control over surface charge and hydrophobicity, as well as facile conjugation to biotags such as peptides, and other functional molecules such as fluorescent dyes. Our proposed research features three specific Aims. These Aims are interrelated and will be performed concurrently, bringing to bear our expertise in synthesis, nanomaterials, and biology. In Aim 1, we will systematically vary the size of the particle and the structure of the monolayer. These studies will be used to create optimized transfection vectors, as well as exploring new vector-DNA unpackaging strategies. We will also explore the conjugation of peptide tags to the particles to provide enhanced uptake and localization of the DNA-MMPC aggregates. Aim 2 describes the strategies that will be used to quantify particle-DNA interactions, transfection efficiency, and toxicity. Aim 3 describes the use of microscopy to determine bottlenecks in the transfection process, providing information that will be used to design enhanced vectors. Rationale for R21 Mechanism. The major innovation of this proposal is the synergistic application of nanotechnology and synthesis to the area of transfection. The proposed research uses the gold core as a scaffold for the presentation of diverse functionalities, providing systems that should provide high transfection coupled with low toxicity. The R21 grant will provide an opportunity to explore the potentialities, directly providing enhanced vectors for in vitro studies. These studies will also lay the groundwork for the development of in vivo gene delivery systems that will be pursued in future studies. [unreadable] [unreadable]